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Satellite images

April 13th, 2009, 16:00

Now that all the excitement of pakarang’s exam success has calmed down, I came back to remembering that this section is one that is under threat due to lack of use - and I wondered if I could perhaps do something about that! With meteorology and oceanography included in the title and the general educational intent in the description, I would be able to occasionally post interesting images received from weather satellites.

Naturally those including Norway, would be likely to be of particular interest!
Here is an interesting image from 5 April 2009 of the Barents Sea which shows cloud streets. As cold air moving from the north over the ice encounters the relatively warmer open sea, clouds have formed from the thermals of rising warm air. With a steady wind, parallel bands of cloud result, aligned with the wind direction.

I have superimposed country boundaries as green lines, making Novaya Zemlya easier to distinguish on the top right of the image, and the ice-bound east side of the Svalbard archipelago on the left. The ice free and cloud free west coast of Spitzbergen is shown in some detail, as is the whole of Norway’s northern coast down to Lofoten at the bottom of the image.

The data, which can be received even on amateur equipment, is from an American instrument (AVHRR - Advanced Very High Resolution Radiometer) on board a European satellite. Operated by EUMETSAT, Europe’s Meteorological Satellite Organisation, Metop-A is a polar-orbiting satellite providing daily world wide coverage.

The image is derived from two channels of data, one from the near infra-red and the other from a heat sensitive waveband. This particular false colouring has been chosen to provide an attractive image while still retaining scientific data.

Comment

I had been wondering about that myself. Looking at the original data in the different channels it is clear that the filament-like structures at the edge of the semi-circular shape are colder. I actually asked about it and will see what some of the more meteorologically-expert folk have to say.

Comment

I had forgotten to report back on this. Further discussion about the details of the feature at the bottom of the image got rather bogged down in flow vectors and the physics of vortices, so I think I’ll just stick to what I might have said in the first place!! The low level air flow from the north has less impetus further south and the effect of the land of the north coast of Norway is to cause warmer air to rise over it. This cools as it gains altitude and the striations at the edge are cirrus cloud formed at the highest level as moisture freezes.

Comment

Some interesting maritime-related data has been obtained from satellites for a number of years, for example radar data from the European Space Agency’s Envisat satellite. Recently reported work based on such data covers topics such as the relationship of NO2 emissions to ship traffic patterns, monitoring of shipping routes and ship distribution in harbours.

Comment

That’s great H-J, and people generally are now getting quite used to seeing satellite imagery in the general media news and weather coverage, for example of severe hurricanes. But other kinds of data applications are less well known. I was hugely impressed by seeing those shipping lanes off the coast of Portugal in that ESA link above in post #5.

Comment

Inspired by the recent off-topic diversion to Bouvet Island – Bouvetřya – (in Veteran ships, Veslekari thread, I thought I would have a look what the weather had been like recently in the remote region of this Norwegian dependency in the South Atlantic!

Here I’m displaying data received from the Metop-A polar-orbiting satellite from around the same time on two successive days. The position of Bouvetřya is indicated by the yellow X.

In this detail from the May-25 image with the island circled, you can see that it appears a similar displayed shade to those small bits of cloud within the otherwise clear area.
As the data I am displaying is from a thermal channel, those clouds and the island are ‘seen’ as being at the same brightness temperature by the satellite’s instrument. This could be either because the ‘solid’ cloud is at the same temperature as the snow-covered island, or because it is actually ‘thinner’ semi-transparent cloud at a lower temperature.

In the detail from the May-26 image, the island is outlined in green (I had selected the country boundary display option in the image processing software). The influence of the island on the cloud is apparent.

Channel 4, from which I derived the colour in this image, is a 10µm thermal channel which has a cadmium mercury telluride cooled detector for infrared heat detection. This has maximum sensitivity where the radiation from objects at earth temperature is a maximum.

Also from the morning of June 25 is a conveniently positioned pass of the NOAA17 satellite:

Comment

Following the floods in the Philippines, I have been receiving satellite images which show further tropical cyclones/typhoons in the general area and the changes occurring over a number of days as these weather systems intensify.

Comment

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